Dear David and Volodymyr,
Thank you for the solution. I was able to install the virtual environment, the necessary packages and convert the snowman.step to inp and flair files.
Below are the steps that helped me on my Ubuntu 24 machine.
sudo apt install python3.12-venv
python3 -m venv --system-site-packages .venv
source .venv/bin/activate
which python
/home/sunil/.venv/bin/python
pip install --upgrade gmsh
pip install meshlib
Then, using the snowman.step from the wherever/geom_mesh_utils/examples/CAD/ directory available when geom_mesh_utils is unpacked,
python3 ~/geom_mesh_utils/FLUKA_mesh_fix.py snowman.step
produces snowman.abaq and a few other files.
Open flair 
input new umesh, and load snowman.abaq in the umesh card and follow the instructions here.
Have fun!
Cheers, Sunil